Remex - A tool for expanding RPG Maker tilesets for use with Tiled's automapping feature.
Map-Tiler - Take a group of "layer images" (walls, floors, etc.) and turn them into a tileset and a Tiled file. Removes duplicate tiles as it imports, has support for generating rooms, and other features. This is very handy when you create maps or levels in layers in a vector or pixel art editor.